1. Field of the Invention
The present disclosure provides a touch sensing device and touch determination method thereof used in the touch sensing device, and more particularly, to prevent the false determination for a touch sensing status of a touch sensing panel caused an external object such as water drop or finger.
2. Description of the Related Art
In order to comply with human intuition, touch sensing devices are widely used in modern electronic products, enabling the user to control electronic products conveniently by means of a touch of a finger or stylus.
Please refer to FIG. 5, when a conventional touch sensing device A1 is started under a mutual capacitive detect mode, the driving and sensing circuit A12 of the touch sensing device A1 measures the capacitive coupling amount (such as the current value, voltage, capacitor or electrical charge amount) at each of all the sensing points A113 between the driving lines A111 and sensing lines A112 of the touch sensing panel A11 at the time no external object (finger or stylus) touches the touch sensing panel A11, and then integrates the measured capacitive coupling amount at each sensing point A113 and the coordinate data of the respective sensing point A113 into a respective 2D sensing information. The processor A13 of the touch sensing device A1 then updates this 2D sensing information to become a reference 2D sensing information and stores this reference 2D sensing information in the memory A14 of the touch sensing device A1.
When an external conductive object touches or covers the touch sensing panel A11 of the touch sensing device A1, the capacitive coupling amount at each sensing point A113 within the touched or covered area is changed. Thus, the processor A13 can read in the reference 2D sensing information from the memory A14, and then subtracts the reference 2D sensing information from each measured 2D sensing information to check the variation of the capacitive coupling amount at each feeling sensing point A113, and to further determine the touch sensing status at each sensing point A113 of the touch sensing panel A11 subject to the variation of the capacitive coupling amount at sensing point.
The processor determines that respective sensing point A113 on the touch sensing panel A11 is not touched by any external electrically conductive object if the capacitive coupling variation of each of all sensing points A113 is between the predetermined positive threshold and the predetermined negative threshold. The processor determines that a sensing point A113 on the touch sensing panel A11 is touched by an external electrically conductive object if the capacitive coupling variation of this sensing point A113 is smaller than the predetermined negative threshold or larger than the predetermined positive threshold.
Please refer to FIG. 6 which is a schematic view of 1D sensing information measured at the area covered by a water drop. The horizontal axis corresponds to the arrangement direction of all sensing points A113 on the driving line A111, the height of respective sensing point A113 on the vertical axis corresponds to different capacitive coupling amount, and the positions of the sensing points A113 and corresponding capacitive coupling amounts are integrated as a waveform of 1D sensing information, and all waveforms of all 1D sensing information on all driving lines A111 are integrated as a 2D sensing information. It is obvious that a negative peak waveform B1 presents on some sensing points A113 covered by the water drop when the touch sensing panel A11 is covered by the water drop. At this time, processor A13 updates the reference 2D sensing information obtained under the covering of the water drop for use as reference 2D sensing information, and a horizontal line waveform B2 will appear on the sensing point A113 within the area covered by the water drop previously when the water drop on the touch sensing panel A11 is removed later and no other external electrically conductive object touch the touch sensing panel A11. Please refer to FIG. 7 which displays a waveform obtained by subtract the horizontal line waveform from the negative peak waveform. The horizontal axis corresponds to the arrangement direction of respective sensing point A113 on the driving line A111, and the vertical axis indicates the variation of capacitive coupling at respective sensing point A113. The processor A13 will determine that the sensing point A113 within the area in which the water drop is removed and no external object touches when the waveform of the 2D sensing information restores to the horizontal line waveform B2 obtained at the time no external object covers the touch sensing panel A11, and a capacitive coupling variation larger than the predetermined positive threshold is measured at the sensing points A113 which is covered by the water drop previously, as shown in FIG. 7, and the processor A13 will execute the touch operation.
Please refer to FIG. 8 and FIG. 9 which display a waveform of 1D sensing information obtained under touch of the finger and a waveform obtained by subtract the horizontal line waveform from a positive peak waveform. When the touch sensing panel A11 is touched by the finger, a positive peak waveform B3 presents at the sensing point A113 within the area touched by the finger. When the processor A13 uses the 2D sensing information obtained under the touch of the finger as the reference 2D sensing information, if the finger leaves the touch sensing panel A11, the waveform of the 2D sensing information restores from the positive peak waveform B3 obtained under the touch of the finger to the horizontal line waveform B2 indicating no covering of the external object, as shown in FIG. 8, and a capacitive coupling variation smaller than the predetermined negative threshold is created at the sensing points A113 within the area touched by the finger previously, so the processor A13 determines the touch sensing panel A11 to be touched and executes the touch operation even if the A113 is not touched by the finger.
Therefore, if the 2D sensing information obtained at the time the water drop covers the touch sensing panel A11 or the finger touches the touch sensing panel A11 is used as the reference 2D sensing information, the capacitive coupling amount of the sensing points A113 being covered by the water drop or the finger will be changed after the abnormal condition on the touch sensing panel A11 is removed, such as removing the water drop or moving the figure apart from the touch sensing panel, the variation of capacitive coupling detected by the processor A13 will be smaller than the predetermined negative determination value or larger than the predetermined positive determination value, and the processor A13 determines that the sensing point A113 is touched by an external object, and make false determination for the touch sensing status of the touch sensing panel A11.
Thus, how to prevent the condition that the touch sensing panel A11 is not touched by any external object but the variation of capacitive coupling is smaller than the predetermined negative threshold or larger than the predetermined positive threshold, is an important subject to study in touchscreen technology.